1. Field of the Invention
The present invention relates to a copying machine which is equipped with an original document feed-through scanning system and is capable of copying a designated area of an original document.
2. Discussion of the Background
There is a copying machine in which an exposure source for exposing an original document and an optical system for imaging the original document are fixed and an original document platen on which an original document is placed moves in order to scan the original document over the fixed exposure source. Since the original document platen moves during a copying operation, there is some apprehension regarding safety with this type of copying machine. Further, the maximum size of the original document which can be copied is limited, because there is some limitation in the size of the original document platen for the same movement and safety reasons.
Therefore, a copying machine in which an original document platen is fixed and an exposure source and a part of an optical system moves for scanning an original document has become popular particularly for the reason that there is no moving unit outside of the machine and that a relatively large original document can be copied.
However, with such a copying machine having a fixed original document platen, it is impossible to copy a whole surface or a part of a lengthy original document, such as for example, a computer output form which is folded, onto a single copysheet with a corresponding length. Consequently, copying is performed in pieces by placing the original document on the original document platen so that a part to be copied is placed at a predetermined position on the original document platen and thus this part is copied onto a standard size copysheet. The original document is then repositioned and another part of the original document is copied to a second sheet of the standard size. This process repeats until the entire original document is copied to a set of standard sized sheets.
In practice, however, it is rather difficult to place a part of an original document at a predetermined position precisely because an original document needs to be placed with a surface to be copied facing the original document platen and thus an operator cannot precisely see how the original document aligns with the original document platen.
There is proposed in Japanese laid open publication 3-44294 an example of a copying machine in which an exposure source, which normally stays at a fixed position, is made to move to a predetermined position for exposing an original document which is transported over that position by means of an original document feeder. Further, this publication proposes to copy a part of a lengthy original document by first starting transport of an original document with depression of a "start" button and then, starting a copying operation with depression of a "copying start" button precisely when a desired part of the original document reaches a position identified by a pointer on the copying machine.
However, with the above arrangement, if an original document is fed with a surface to be copied facing downwards it is impossible for an operator to determine when the part to be copied reaches the pointer. Consequently, when to start a copying operation cannot be determined with any degree of accuracy. Therefore, generally, a mark is put on the back side of an original document at a position corresponding to a leading edge of a part to be copied. The operator depresses the copying start button when the mark reaches a predetermined position thereby improving copying accuracy. It is time-consuming, however, to put such a mark on an original document, especially when the volume of copying is large. Further, copying accuracy may be jeopardized by a risk that a mark is put in a wrong position. Accordingly, this copying approach is suboptimal because it is manually intensive and subject to copying inaccuracies.
When copying a designated area of each of a plurality of original documents each having a designated area at an identical position to the other original documents, it is troublesome to depress a copying start button at precisely the correct time for each of the plurality of original documents.
Further, if a speed of original document transport is as fast as 20-30 cm/sec, for example, as in most modern copying machines, it is almost impossible to designate a copying start position precisely. Even with a copying machine with a speed of 2-3 cm/sec, it is rather difficult to designate a copying start position precisely. Furthermore, a copy machine with such a slow speed is not suitable for practical use.